I plan to add an extension to std.format, namely a new format character with the meaning of producing a source code literal. Or more formally, the following snippet should work for every type this extension will support:

enum a = <something>;
enum b = mixin(format!"%S"(a));

static assert(a == b && is(typeof(a) == typeof(b)));

(Please note, that even for floats a == b should hold for all values, but NaNs; I plan to use RYU for this.)

The big question is now, which character to use. I thought of %S like source code literal. Andrei suggested %D like D literal. Both ideas have the disadvantage of using uppercase letters, which would break the of uppercase letters meaning that the output uses uppercase instead of lowercase (i.e. 1E10 instead of 1e10).

A first idea of a lowercase literal might be %l but this might easily be confused with %I and %1 (both don't exist); and also l is used in C's printf for long which we luckily don't need here. Anyway I fear confusion.

What do you think? Which letter would be best?

On Friday, 30 April 2021 at 07:10:38 UTC, Berni44 wrote:

Actually S is already used. The only specifier that is "free" would be D. But, what's so bad with using L? 🤔

On Friday, 30 April 2021 at 07:20:11 UTC, Imperatorn wrote:

Huh, where? Not in std.format...

On Friday, 30 April 2021 at 08:02:44 UTC, Berni44 wrote:

No I meant for [w]printf

https://docs.microsoft.com/en-us/cpp/c-runtime-library/format-specification-syntax-printf-and-wprintf-functions

On Friday, 30 April 2021 at 07:10:38 UTC, Berni44 wrote:

If this would be unique to mixins, then %m, if not, L(iteral) or D(literal).

On Friday, 30 April 2021 at 21:11:55 UTC, H. S. Teoh wrote:

Of course, there are limits to this. I intend to implement it for bools, integers, floats, characters, strings and enums. I think it will also be possible to implement it for (associative) arrays, as long as the elements can be implemented like this. Structs, classes, interfaces and unions should implement it in their toString functions. I wouldn't go so far to provide generic code for them. With that we'll indeed run into problems. (Maybe with the exception of structs with default constructor.) I haven't made up my mind about pointers yet.

And well functions, delegates and lambdas? Functions aren't supported by std.format at all and the implementation of delegates is broken and useless and should be removed (in my opinion).

On Friday, 30 April 2021 at 07:10:38 UTC, Berni44 wrote:

Would %q work? In reference to token strings:

enum a = <something>;
enum b = mixin(format!"%q"(a));
enum c = mixin(q{<something>});

static assert(a == b && is(typeof(a) == typeof(b)));
static assert(c == b && is(typeof(c) == typeof(b)));

— Bastiaan.